arXiv subjects

A. De Rujula

Publications and source records attributed to A. De Rujula.

46 records · Page 3Linked to original sources

arXiv2002

Optical and X-ray Afterglows in the Cannonball Model of GRBs

The Cannonball Model is based on the hypothesis that GRBs and their afterglows are made in supernova explosions by relativistic ejecta similar to the ones observed in quasars and microquasars. Its predictions are simple, and analytical in fair approximations. The model describes well the properties of the $γ$-rays of GRBs. It gives a very simple and extremely successful description of the optical and X-ray afterglows of {\it all} GRBs of known redshift. The only problem the model has, so far, is that it is contrary to staunch orthodox beliefs.

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arXiv2001

High-energy neutrinos and hard $γ$-rays in coincidence with Gamma Ray Bursts

The observations suggest that $γ$-ray bursts (GRBs) are produced by jets of relativistic cannonballs (CBs), emitted in supernova (SN) explosions. The CBs, reheated by their collision with the SN shell, emit radiation and Doppler-boost it to the few-hundred keV energy of the GRB's photons. Chaperoning the GRB, there should be an intense flux of neutrinos of a few hundreds of GeV energy, made in $π^\pm$ decays: the SN shell acts as a dump of the beam of CBs. The $ν$ beam carries almost all of the emitted energy, but is much narrower than the GRB beam and should only be detected in coincidence with the small fraction of GRBs whose CBs are very precisely pointing to us. The $π^0$s made in the transparent outskirts of the SN shell decay into energetic $γ$-rays (EGRs) of energy of ${\cal{O}}$(100) GeV. The EGR beam, whose energy fluence is comparable to that of the companion GRB, is as wide as the GRB beam and should be observable, in coincidence with GRBs, with existing or planned detectors.

hep-ph↗

arXiv2001

The Cannonball Model of Gamma Ray Bursts: high-energy neutrinos and $γ$-rays

Recent observations suggest that $γ$-ray bursts (GRBs) and their afterglows are produced by jets of highly relativistic cannonballs (CBs), emitted in supernova (SN) explosions. The CBs, reheated by their collision with the shell, emit radiation that is collimated along their direction of motion and Doppler-boosted to the typical few-hundred keV energy of the GRB. Accompanying the GRB, there should be an intense burst of neutrinos of a few hundreds of GeV energy, made by the decay of charged pions produced in the collisions of the CBs with the SN shell . The neutrino beam carries almost all of the emitted energy, but is much narrower than the GRB beam and should only be detected in coincidence with the small fraction of GRBs whose CBs are moving very close to the line of sight. The neutral pions made in the transparent outskirts of the SN shell decay into energetic $γ$-rays (EGRs) of energy of ${\cal{O}}$(100) GeV. The EGR beam, whose energy fluence is comparable to that of the companion GRB, is as wide as the GRB beam and should be observable, in coincidence with GRBs, with existing or planned detectors. We derive in detail these predictions of the CB model.

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arXiv2001

The Cannonball Model of Gamma Ray Bursts: Lines in the X-Ray Afterglow

Recent observations suggest that gamma-ray bursts (GRBs) and their afterglows are produced by jets of highly relativistic cannonballs (CBs), emitted in supernova explosions. The fully ionized CBs cool to a temperature below 4500 K within a day or two, at which point electron-proton recombination produces an intense Lyman-$α$ emission. The line energy is Doppler-shifted by the CBs' motion to X-ray energies in the observer's frame. The measured line energies, corrected for their cosmological redshift, imply Doppler factors in the range 600 to 1000, consistent with those estimated -in the CB model- from the characteristics of the $γ$-ray bursts. All other observed properties of the lines are also well described by the CB model. Scattering and self-absorption of the recombination lines within the CB also produce a wide-band flare-up in the GRB afterglow, as the observations indicate. A very specific prediction of the CB model is that the X-ray lines ought to be narrow and move towards lower line energies as they are observed: their current apparently large widths would be the effect of time integration, and/or of the blending of lines from CBs with different Doppler factors.

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arXiv2000

Fat Brane Phenomena

Gravitons could permeate extra space dimensions inaccessible to all other particles, which would be confined to ``branes''. We point out that these branes could be ``fat'' and have a non-vanishing width in the dimensions reserved for gravitons. In this case the other particles, confined within a finite width, should have ``branon'' excitations. Chiral fermions behave differently from bosons under dimensional reduction, and they may --or may not-- be more localized than bosons. All these possibilities are in principle testable and distinguishable, they could yield spectacular signatures at colliders, such as the production of the first branon excitation of $γ$'s or $Z$'s, decaying into their ground state plus a quasi-continuum of graviton recurrences. We explore these ideas in the realm of a future lepton collider and we individuate a {\it dimensiometer}: an observable that would cleanly diagnose the number of large ``extra'' dimensions.

hep-ph↗

arXiv2000

The atmospheric neutrino anomaly without maximal mixing?

We consider a pattern of neutrino masses in which there is an approximate mass degeneracy between the two mass eigenstates most coupled to the $ν_μ$ and $ν_τ$ flavour eigenstates. Earth-matter effects can lift this degeneracy and induce an effectively maximal mixing between these two generations. This occurs if $ν_e$'s contain comparable admixtures of the degenerate eigenstates, even rather small ones. This provides an explanation of the atmospheric neutrino anomaly in which the {\it ab initio} introduction of a large mixing angle is not required. To test this possibility we perform a novel and detailed analysis of the 52 kiloton-year SuperKamiokande data, and we find that in a large region of parameter space the corresponding confidence levels are excellent. The most recent results from the Chooz reactor experiment, however, severely curtail this region, so that the conventional scenario with nearly maximal mixing angles --which we also analyse in detail-- is supported by the data.

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arXiv1998

On the photon constituency of protons

We argue that existing measurements of ep collisions at HERA --in which an energetic photon is made via a QED `Compton' subprocess-- can provide rather detailed information on the photonic parton density of the proton. This function and its deviations from Bjorken scaling should be measurable, allowing for an interesting test of the theory. The photonic distribution function and its gluonic counterpart should show a strikingly different evolution with momentum scale.

hep-ph↗

arXiv1998

Neutrino oscillation physics with a neutrino factory

Data from atmospheric and solar neutrinos indicate that there are at least three neutrino types involved in oscillation phenomena. Even if the corresponding neutrino mass scales are very different, the inevitable reference to mixing between more than two neutrino types has profound consequences on the planning of the accelerator experiments suggested by these results. We discuss the measurement of mixing angles and CP phases in the context of the neutrino beam emanating from a {\it neutrino factory}: the straight sections of a muon storage ring. We emphasize the importance of charge identification. The appearance of wrong sign muons in a long baseline experiment may provide a powerful test of neutrino oscillations in the mass-difference range indicated by atmospheric-neutrino observations.

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arXiv1997

A Matter-Antimatter Universe?

We ask whether the universe can be a patchwork consisting of distinct regions of matter and antimatter. We demonstrate that, after recombination, it is impossible to avoid annihilation near regional boundaries. We study the dynamics of this process to estimate two of its signatures: a contribution to the cosmic diffuse gamma-ray background and a distortion of the cosmic microwave background. The former signal exceeds observational limits unless the matter domain we inhabit is virtually the entire visible universe. On general grounds, we conclude that a matter-antimatter symmetric universe is empirically excluded.

astro-ph↗

arXiv1997

Scars on the CBR?

We ask whether the universe can be a patchwork consisting of distinct regions of matter and antimatter. In previous work we demonstrated that post-recombination matter-antimatter contact near regional boundaries leads to an observable (but unobserved) gamma-ray flux for domain sizes of less than a few thousand Mpc, thereby excluding such domains. In this paper we consider the pre-recombination signal from domains of larger size.

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